Several diseases and conditions of the posterior segment of the eye threaten vision. Age related macula degeneration (ARMD), choroidal neovascularization (CNV), retinopathies (e.g. diabetic retinopathy, vitreoretinopathy), retinitis (e.g., cytomegalovirus (CMV) retinitis), uveitis, macular edema, glaucoma, and neuropathies are several examples.
These, and other diseases, can be treated by injecting drug formulations into the eye. Such injections are typically manually performed using a conventional syringe and needle. FIG. 1 is a perspective view of a prior art syringe used to inject drugs into the eye. In FIG. 1, the syringe includes a needle 105, a luer hub 110, a chamber 115, a plunger 120, a plunger shaft 125, and a thumb rest 130. As is commonly known, the drug to be injected is located in chamber 115. Pushing on the thumb rest 130 axially displaces the plunger, causing the plunger 120 to expel the drug through needle 105.
In using such a syringe, the surgeon is required to pierce the eye tissue with the needle, hold the syringe steady, and actuate the syringe plunger (with or without the help of a nurse) to inject the drug formulation into the eye. However, such a configuration results in uncontrolled flow rates. Further, reading the vernier is subject to parallax error which may affect the precision and accuracy of the injected volume. Tissue damage may occur due to an “unsteady” injection. Reflux of the drug may also occur when the needle is removed from the eye.
Other known devices include an electromechanical actuator to generate linear displacement of a piston, which in turn engages a plunger within a drug chamber. The plunger expels the drug formulation housed in the drug chamber through a needle. In such a design, a user activates a button through a controller that forces/instructs the actuator to move forward. While this design has more consistent flow rate control than the syringe design, such a system is costly and mechanically challenging to manufacture, especially for designs that include disposable tip segments that may be used with a reusable portion. Indeed, proper alignment of the actuator components between the disposable and reusable portions is critical, thereby requiring tight tolerances. Further, the electromechanical actuator arrangement also has an increased chance of failure in view of the additional moveable parts required. The electromechanical actuator assembly also adds both weight and length to the device.